Pulp molding



Jan. 12, 1960 R. wELLs PULP MoLnING Filed sept, 2a, 195e III J4 INVENTOR Royer Wells BY KQRL L). T :ocxs

ATTORNEY PULP MoLnlNG Roger Wells, Plnttsbnrg, N.Y., assig'nor to Diamond National Corporation, a corporation of Delaware Application September 28, 1956, Serial No. 612,696

Claims. (Cl. 162-411) This invention relates to pulp molds, and more particularly to pulp molds fhaving drainage traps therein.

In the manufacture of molded pulp articles, such as pie plates or other food containers, it is customary to form an initially molded article, known as a preform, by dipping a foraminous mold into liquid pulp slurry, which is `usually a suspension of pulp fibers in water, and simultaneously applying suction to the mold to cause a layer of wet pulp fibers to be deposited thereon; subsequently the resultant pulp preform -is completely dried and finished to produce the molded article desired. Suction is continued while the mold is advanced from the initial forming position in the pulp slurry to an article discharge position, which may be located adjacent to a conveyor belt moving toward a final drying chamber. The suction extracts most of the excess liquid from the wet preform by the time the mold reaches the article discharge position, but a small quantity of residual liquid usually remains inside the mold.

The molded pulp preform is ejected from the mold at the discharge station by stopping the suction, and then blowing or sucking the preform therefrom. In the systems employed heretofore, any small quantity of residual liquid which remained in the mold was likewise blown or sucked out, and frequently this liquid was blown upon the preform being ejected. Usually the liquid was blown upon one edge of the preform, making lthis edge limp and soggy. Since at this stage of its lwere defective due to blemishes, collapsed edges, or

warping caused by lack of uniformity in drying characteristics.

In my copending application Serial No. 612,855 filed September 28, 1956, there is described and claimed a pulp mold having a drainage trap designed to prevent excess liquid from being blown upon a preform being discharged. This mold comprises a chambered body .connected to a source of' suction, a perforated forming .plate covering the chambered body, and a plurality of standpipes mounted in the perforations in the forming plate. The standpipes project upwardly into the cham- -bered body a distance suticient to prevent residual liqfrom escaping through the perforations during the discharge operation. lmounted in each of the perforations in the plate,`or only One of the standpipes may be the;perforations in a certain portion of the plate may be provided with the standpipes.

In` thejmanufacture of this mold, many separate operationsare-required to fit each of the standpipes individually into the perforations in the forming plate. First,

United States Patent O thin-walled metal pipes must be cut into short lengths, then the perforations in the forming plate must be enlarged by drilling to accommodate the short pipes, and finally each standpipe must be seated individually by separate soldering or threading operations. Hence, considerable labor and expense is involved in making such molds, and their structure is relatively complex.4

An object of the present invention is to simplify the structures of pulp molds having drainage traps and the methods of manufacturing such molds. v

Another object of the invention is to provide new and improved pulp molds having drainage traps. v.

Other objects and the nature and advantages of the instant invention will be apparent from lthe following description taken in conjunction with the accompanying drawings, wherein:

Fig. 1 is a vertical sectional view of a pulp mold embodying the invention;

Fig. 2 is a top plan view, taken along the line 2--2 of Fig, 1, showing the inner surface of the forming plate of the mold; and

Fig. 3 is a vertical sectional view of a portion of a pulp mold forming a second embodiment of the invention.

In the embodiment of the invention illustrated in Figs. 1 and 2, a foraminous mold indicated generally by the numeral 10 is movable vertically into and out of a tank (not shown) containing liquid pulp slurry. The mold 10 includes a tapered chambered body 12 connected at its upper end to a source (not shown) of suction, and having a ange 14'formed on the open lower end thereof, A perforated forming plate 16 covers the open lower end of the chambered body `12. The plate 16 has a reduced rim 18 which is secured to the flange 14 on the chambered body 12. A plurality of transverse perforations 20-20 are located at uniform intervals over the entire area of the plate 16. The outer or forming face of the plate is covered by a coextensive finestraining screen 22. An endless band 24 secured to the rim 18 of the plate 16 by a plurality of bolts 26-26 holds the screen 22 snugly against the plate 16.

Molded pulp articles are formed initially by applying suction to the chambered body 12 while the mold 10 is lowered and immersed in liquid pulp slurry, thereby causing a 'layer of wet pulp fibers forming a preform to be deposited on the screen 22. Excess water is extracted from the wet preform by continuing the suction while the mold 10 is being elevated above the slurry and advanced to the discharge station. The preform is ejected by stopping the suction and blowing or sucking the preform from the mold. Usually compressed air is admitted to the chambered body `12 for this purpose.

At this time the residual water which is in the interior of the chambered body 12 may be blown out through the perforations 20-20 and onto the molded article being discharged, unless drainage traps are provided in the interior of the mold.

In my copending application Serial No. 612,855, previously referred to herein, drainage traps are formed by mounting a plurality of standpipes in the perforations in the forming plate. Said standpipes are short lengths of thin-Walled pipe which are fitted individually Iby soldering or threading them into each of the perfofrations.

In accordance with the present invention, perforated projections which function as standpipes are formed integrally in ush sealing relation with the inner side of the forming plate, resulting in a considerable simplification of the structure and the mode of manufacture of the molds. A plurality of projections 28-28 may be formed on the plate 16 by first casting this plate in one solid imperforate unit, and then milling spaced, parallel,

'transverse grooves 30-30 'and similarly spaced, parallel, l

longitudinal 4grooves 32-32 therein. The grooves 30--30` Y and 32-32 intersect perpendicularly, leaving the projections 28-28 formed between them. Then the perforations Ill-'40 may be formed by simultaneously drilling holes longitudinally through the projections 2828. Although the projections 28-28 and the grooves 30-30 and 3'2-32 appear square in cross-section kin Figs. 1 and 2, Ait `is evident that they may be rounded or tapered to produce other congurations. Furthermore, instead of forming 'the projections 28-28 by milling the grooves 30--30 and 32-32 in the plate 16, .these projections 28--128 may be `formed during the original casting of the plate 16. In such vrcase, the projections 28-28 may be made perfectly cylindrical, 'and they may be finished merely by drilling `longitudinal holes therethrough to form the perforations 'Z0- 20.

The forming plate :16 'is 'considerably Vthicker than conventional forming plates, such as the kplates disclosed in my aforesaid copending application Serial No. 612,855. Such .plates are usually made of cast brass or bronze. In order to reduce the weight of the plate 16 it may be made of cast aluminum or 'a suitable tough, strong, thermosetting plastic compound. lIt is believed that such plastic compounds are so well known that they need not be specified further. In one practical example of a mold embodying the invention, the grooves 30-30 and 32-32 were milled to a depth of about inch, and they were about f4 inch wide with centers spaced about 'l inch apart. In some instances, it may be desirable to increase the depth `of the grooves to about 2 inches, Ithereby creating a corresponding increase in the length 'of the projections and the size of the drainage traps surrounding them.

In the embodiment of the invention illustrated in Fig. 3, the :inner side of a metallic forming plate 50 is covered by a thick layer 52 of 4a thermosetting plastic compound. The layer 52 is molded onto the plate 50 and it is rmly Aadherent thereto. A plurality of projections 54-54 are molded integrally with the plastic layer 52, and this is preferably done at the same time that the layer 52 is molded onto the plate 50. Any suitable well known thermosetting plastic compound may be employed for this purpose. The layer 50 and its .projections y54-54 may be formed lin a single operation by .placing `a mass or slab of the plastic compound on the inner side of fthe plate 50 `before 'drilling any perforations therein, and Ycompressing the same between heated dies which are .properly contoured to form ,the projections as well as the layer 52. In this manner, the projections may be made round or `square in cross-section, yand they may be vmade either tapered or uniform in thickness throughout their length. Finally, a plurality of perforations 56-56 passing longitudinally through the :projections 54-54 and thence transversely through the plate 50 may be formed i simultaneously by drilling parallel kholes through these members. The .perforations 56-56 extend entirely through the projections 54-54 and the plate 50 to ,the outer or forming face of the plate 50.

For the embodiment of the invention shown in Fig. 3,

the metallic plate 50 may be an ordinary cast bronze forming plate `having vits inner side covered and filled by the plastic layer 52. The outer or forming face of the vplate 50 is covered by a coextensive line-straining screen 58, which is secured thereto by a band 60 and a plurality of bolts 62-'61 The composite laminated plate .50 and plastic layer 52 are designed to cooperate with a chambered body, similar to the body 12 shown in Fig. l, toform a complete foraminous mold capable of functioning in the same manner as the mold in the manu- :facture of molded pulp articles.

It will be obvious to those lskilled in the art that vari- -ous changes may be made without departing from the spirit-of the invention and therefore `the invention is ln'ot limited to what is shown in the drawings vand described in the specification but only as indicated in vthe appended What is claimed is:

1. A mold for forming pulp articles by deposition from liquid pulp slurry and from which the articles are subsequently discharged by blowing or sucking them from the mold, said mold comprising a chambered body adapted to be connected to la source of suction, a perforated forming plate covering the chambered body, said plate having a plurality of transverse perforations spaced uniformly over its entire area, and a plurality of longitudinally perforated projectionslmolded integrally in ush sealing relation on the inner side of the forming plate in positions corresponding to and aligned with Vthe perforations therein, said projections extending upwardly into the chambered body a distance sufficient to prevent residual liquid from escaping through the perforations.

2. A mold for forming pulp articles by deposition from liquid pulp slurry land from which the articles are subse` quently discharged by blowing or sucking them from the mold, said mold comprising a chambered body adapted to be connected to a source of suction, and a perforated forming plate covering the chambered body, the inner face of said plate vhaving cut therein a plurality of intersecting grooves which are sufficiently deep to form between them a plurality of elongated projections in Hush sealing relation with the inner face of the plate positioned at uniformly spaced intervals over the entire area of the plate and extending upwardly into the chambered body, each of said projections having a perforation extending entirely therethrough to the outer forming face of the plate, whereby residual liquid trapped in the kgrooves is prevented from escaping through the perforations.

3. A mold for forming pulp articles by deposition from liquid pulp slurry `and from which the .articles are subsequently discharged by blowing or sucking them from the mold, said Vmold comprising a chambered body adapted to be connected to a source of suction, and a perforated forming .plate covering the chambered body, the inner face of said plate having milled therein a plurality of spaced parallel transverse grooves and a plurality of spaced parallel longitudinal .grooves perpendicularly intersecting ythe transverse grooves at uniform intervals over :the'entire area of the plate and leaving between the grooves `a plurality of velongated projections in ush sealing relation with the inner face lof the plate and extending upwardly into the chambered body, each of said vprojections having a perforation extending entirely therethrough to the outer forming face of the plate, said grooves being sufliciently deep to form drainage traps which prevent residual liquid from escaping through the perforations.

4. A mold for forming pulp articles by deposition from liquid pulp slurry and V'from which the articles are subsequently discharged by blowing or sucking them from the mold, said mold comprising a chambered body adapted to be connected to a source of suction, a perforated metallic forming plate covering the chambered body, said -plate having a plurality of transverse perforations spaced uniformly `over yits entire area, a relatively thick molded layer of a thermosetting plastic compound covering the inner face of said metallic plate, and a plurality of perforated projections molded integrally in ush sealing relation on the vplastic layer in positions corresponding to and aligned with the perforations in the plate, said projections extending upwardly into the chambered body a distance suflcient to form drainage traps for preventing residual liquid from Iescaping 'through the perforations.

5. A mold for forming pulp articles by deposition from liquid vpulp slurry and from which the articles are subsequently discharged by blowing or sucking them from the mold, said mold comprising a chambered body adapted to be connected to `a source of suction, a perforated metallic forming plate covering Vthe chambered body, said plate having a plurality of transverse perforations spaced uniformly over its entire area, a relatively thick molded layer of a thermetting plastic compound covering the inner face of said metallic plate, and a plurality of cylindrical standpipes molded integrally in 5 flush sealing relation on the inner side of the plastic layer, said standpipes being aligned with the perforations in the plate and extending upwardly into the chambered body a distance sucient to form drainage traps for preventing residual liquid from escaping through the perfora- 10 tions.

References Cited in the le of this patent UNITED STATES PATENTS 1,795,519 Sheldon Mar. 10, 1931 l5 f 6 Chuse May 24, 1938 Grol Mar. 7, 1939 Chaplin June 27, 1939 Lindabl Mar. 17, 1942 Fuller May 2, 1944 Vinal July 23, 1946 Hillbom Feb. 4, 1947 McGinnis Mar. 18, 1947 Randall June 10, 1952 Walther May 3, 1955 Lambert Sept. 27, 1955 Emery Dec. 4, 1956 

